Plant and animal pathogenic bacteria can suppress host immunity by injecting type III secreted effector (T3SE) proteins into host cells. However, T3SEs can also elicit host immunity if the host has evolved a means to recognize the presence or activity of specific T3SEs. The diverse YopJ/HopZ/AvrRxv T3SE superfamily, which is found in both animal and plant pathogens, provides examples of T3SEs playing this dual role. The T3SE HopZ1a is an acetyltransferase carried by the phytopathogen Pseudomonas syringae that elicits effector-triggered immunity (ETI) when recognized in Arabidopsis thaliana by the nucleotide-binding leucine-rich repeat (NB-LRR) protein ZAR1. However, recognition of HopZ1a does not require any known ETI-related genes. Using a forward genetics approach, we identify a unique ETI-associated gene that is essential for ZAR1-mediated immunity. The hopZ-ETI-deficient1 (zed1) mutant is specifically impaired in the recognition of HopZ1a, but not the recognition of other unrelated T3SEs or in pattern recognition receptor (PRR)-triggered immunity. ZED1 directly interacts with both HopZ1a and ZAR1 and is acetylated on threonines 125 and 177 by HopZ1a. ZED1 is a nonfunctional kinase that forms part of small genomic cluster of kinases in Arabidopsis. We hypothesize that ZED1 acts as a decoy to lure HopZ1a to the ZAR1-resistance complex, resulting in ETI activation.ZED1-related kinase | ZRK | hypersensitive response

Nucleotide-binding domain and leucine-rich repeat domain-containing (NLR) proteins are sentinels of plant immunity that monitor host proteins for perturbations induced by pathogenic effector proteins. Here we show that the Arabidopsis ZAR1 NLR protein requires the ZRK3 kinase to recognize the Pseudomonas syringae type III effector (T3E) HopF2a. These results support the hypothesis that ZAR1 associates with an expanded ZRK protein family to broaden its effector recognition spectrum.

Measuring the extent and severity of disease is a critical component of plant pathology research and crop breeding. Unfortunately, existing visual scoring systems are qualitative, subjective, and the results are difficult to transfer between research groups, while existing quantitative methods can be quite laborious. Here, we present plant immunity and disease image-based quantification (PIDIQ), a quantitative, semi-automated system to rapidly and objectively measure disease symptoms in a biologically relevant context. PIDIQ applies an ImageJ-based macro to plant photos in order to distinguish healthy tissue from tissue that has yellowed due to disease. It can process a directory of images in an automated manner and report the relative ratios of healthy to diseased leaf area, thereby providing a quantitative measure of plant health that can be statistically compared with appropriate controls. We used the Arabidopsis thaliana-Pseudomonas syringae model system to show that PIDIQ is able to identify both enhanced plant health associated with effector-triggered immunity as well as elevated disease symptoms associated with effector-triggered susceptibility. Finally, we show that the quantitative results provided by PIDIQ correspond to those obtained via traditional in planta pathogen growth assays. PIDIQ provides a simple and effective means to nondestructively quantify disease from whole plants and we believe it will be equally effective for monitoring disease on excised leaves and stems.

Pseudomonas syringae is a bacterial phytopathogen that utilizes the type III secretion system to inject effector proteins into plant host cells. Pseudomonas syringae can infect a wide range of plant hosts, including agronomically important crops such as tomatoes and beans. The ability of P. syringae to infect such numerous hosts is caused, in part, by the diversity of effectors employed by this phytopathogen. Over 60 different effector families exist in P. syringae; one such family is HopF, which contains over 100 distinct alleles. Despite this diversity, research has focused on only two members of this family: HopF1 from P. syringae pathovar phaseolicola 1449B and HopF2 from P. syringae pathovar tomato DC3000. In this study, we review the research on HopF family members, including their host targets and molecular mechanisms of immunity suppression, and their enzymatic function. We also provide a phylogenetic analysis of this expanding effector family which provides a basis for a proposed nomenclature to guide future research. The extensive genetic diversity that exists within the HopF family presents a great opportunity to study how functional diversification on an effector family contributes to host specialization.

Gram-negative bacterial pathogens inject type III secreted effectors (T3SEs) directly into host cells to promote pathogen fitness by manipulating host cellular processes. Despite their crucial role in promoting virulence, relatively few T3SEs have well-characterized enzymatic activities or host targets. This is in part due to functional redundancy within pathogen T3SE repertoires as well as the promiscuity of individual T3SEs that can have multiple host targets. To overcome these challenges, we generated and characterized a collection of yeast strains stably expressing 75 T3SE constructs from the plant pathogen Pseudomonas syringae . This collection is devised to facilitate heterologous genetic screens in yeast, a non-host organism, to identify T3SEs that target conserved eukaryotic processes. Among 75 T3SEs tested, we identified 16 that inhibited yeast growth on rich media and eight that inhibited growth on stress-inducing media. We utilized Pathogenic Genetic Array (PGA) screens to identify potential host targets of P. syringae T3SEs. We focused on the acetyltransferase, HopZ1a, which interacts with plant tubulin and alters microtubule networks. To uncover putative HopZ1a host targets, we identified yeast genes with genetic interaction profiles most similar ( i.e. , congruent) to the PGA profile of HopZ1a and performed a functional enrichment analysis of these HopZ1a-congruent genes. We compared the congruence analyses above to previously described HopZ physical interaction datasets and identified kinesins as potential HopZ1a targets. Finally, we demonstrated that HopZ1a can target kinesins by acetylating the plant kinesins HINKEL and MKRP1, illustrating the utility of our T3SE-expressing yeast library to characterize T3SE functions.

A glycoprotein was isolated from bovine erythrocytes which has 20% carbohydrate and migrates on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a single band. This glycoprotein carries the reactivity of bovine erythrocytes with Paul-Bunnell heterophile antibody of infectious mononucleosis. This bovine glycoprotein was coupled to carboxyl-modified latex particles with water-soluble carbodiimide. The resulting reagent was then used to develop a new test for the detection of infectious mononucleosis antibody. The bovine erythrocyte glycoprotein-latex reagent is more stable than sheep or horse erythrocytes, the traditional reagents for detection of infectious mononucleosis antibody. This new reagent is used in a direct slide test; no preabsorption of the sera is necessary. In the present study the glycoprotein-latex reagent compared favorably in terms of sensitivity and specificity with two standard tests for infectious mononucleosis antibody. Ninety-nine serum samples were tested. Agreement of the latex test with a stabilized horse erythrocyte spot test was 90%. Ten samples were weakly positive with the latex test and negative with the horse cell test. Only one of these was also positive with an enzyme-treated sheep cell test. This latter test was somewhate more sensitive than the latex test.

We have recently described the presence of a guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.21 inhibitor (GCI) in an aqueous extract of the balsam pear (Momordica charantia abbreviata). Because the guanylate cyclase-cyclic GMP system is thought to be involved in cell growth, DNA and RNA synthesis, and possibly malignant transformation, we examined the effect of the aqueous extract containing GCI on an undifferentiated adenocarcinoma of the rat prostate and concanavalin-A-stimulated [3Hlthymidine incorporation into cultured splenic lymphocytes, a process thought to be mediated by cyclic GMP. The results demonstrate that the extract of the balsam pear blocks both the growth of the rat prostatic adenocarcinoma in vitro and [3H thymidine incorporation into DNA. DNA histograms from flow cytometry indicated that the extract containing GCI inhibited in the G2 + M phase of the cell cycle, a presumed locus of cyclic GMP effects. In addition, guanylate cyclase activity was significantly greater in the tumor than normal prostate tissue and was decreased by the extract containing GCL Cyclic GMP levels in the tumor in culture were also decreased by addition of the extract. It remains to be determined whether or not the anti-tumor agent and GCI are the same substance.The balsam pear (Momordica charantia abbreviata) is a plant that grows wild throughout subtropical regions of the world, including Florida and the Gulf Coast of the United States; We have recently reported (1) that an aqueous extract of the ripe fruit of the balsam pear contains an inhibitor of guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2], the enzyme that catalyzes the conversion of guanosine triphosphate (GTP) to guanosine 3',5'-monophosphate (cyclic GMP). The guanylate cyclase inhibitor (GCI) blocked both the basal activity of guanylate cyclase and the activation of guanylate cyclase by nitroso chemical carcinogens (1). The latter finding was of particular interest because current evidence suggests that the major role of cyclic GMP in cell biology is concerned with cell growth, DNA and RNA synthesis, and possibly malignant transformation (2-12). A recent investigation by Zeilig and Goldberg (12), using Novikoff rat hepatoma cells, showed that, as these synchronized cells entered mitosis, cellular cyclic GMP levels rose and cellular adenosine 3',5'-monophosphate (cyclic AMP) levels declined. As the cells entered the quiescent stages of growth, the ratios of these nucleotides reversed, with cyclic AMP levels rising and cyclic GMP levels reaching their nadir. It seemed worthwhile, therefore, to determine the effects of the extract on both tumor cells and normal cells.In the present investigation we utilized cell cultures of an undifferentiated adenocarcinoma of the rat prostate, observed MATERIALS AND METHODS Cell Source and Cultivation. The prostatic adenocarcinoma cells in tissue culture were derived from the hormone-responsive G subline of the Dunning R3327 tumor. A subcutaneous G tumor in the 22nd in vivo passag...

Successful pathogenesis requires a number of coordinated processes whose genetic bases remain to be fully characterized. We utilized a high-throughput, liquid media-based assay to screen transposon disruptants of the phytopathogen Pseudomonas syringae pv. maculicola ES4326 to identify genes required for virulence on Arabidopsis. Many genes identified through this screen were involved in processes such as type III secretion, periplasmic glucan biosynthesis, flagellar motility, and amino acid biosynthesis. A small set of genes did not fall into any of these functional groups, and their disruption resulted in context-specific effects on in planta bacterial growth.